Spectral propagation-based x-ray phase-contrast imaging

Abstract

Propagation-based imaging is an X-ray phase-contrast method that does not require any additional optical elements in the imaging system. Instead, phase-contrast effects are observed as measurable intensity variations after an incident X-ray wave field has propagated some distance between the object and plane of detection. Subsequent phase-retrieval processing of the recorded images is a necessary step in order to obtain quantitative information and can greatly increase the image signal-to-noise ratio, in particular in computed tomography. Most commonly this is done by approximating the object as a single material, which cannot always be justified. An example of this is the presence of bones and soft-tissues in biomedical imaging, which motivated the work presented here. We developed the combination of spectral X-ray imaging and propagation-based X-ray phasecontrast imaging to overcome the limitations of a single-material approximation. The addition of spectral data enables phase-retrieval on multi-material objects, as well as the use of processing methods well-known from conventional dual-energy imaging, such as material decomposition, virtual monochromatic images and effective atomic-number mapping. Here, we present first computed tomography results of spectral propagation-based phase-contrast. We discuss how the phase retrieval process can be interpreted as low- and high-pass filters. Lastly, we take a look at current and future technological challenges, and the potential application areas of spectral propagation-based phase-contrast imaging.